Thanks for visiting the forum Joost.
I started this thread to have a whinge about Google, but mainly to warn others about what happened to us.
It didn't occur that my messed up meta titles may have anything to do with WP SEO or WPSEO Video, and I didn't want to waste your time; if this was not possibly caused by either of your plugins.
I am still not 100% sure about this.
Yesterday, I added Google+ Publisher & Authorship markup to our home page - as recommended above by mAsT3RpEE.
I then deactivated WPSEO Video.
About the same time you pushed out an update for WP SEO, so I updated.
Within a couple of hours, our meta title and description was displaying correctly in Google serps - after being messed up since 10th June!
You can see that Google has re-indexed our home page, because my mug-shot (authorship) appears next to it. (I have since removed authorship from this page). This is not a cached result either; because I added meta name="robots" content="noarchive" to our header.php
I have no idea where this wrong title/description was coming from, but it only appeared in Google serps - not Yahoo or Bing.
If there was something in the database causing problems; the only SEO plugin previously used was 'Headspace2'.
I would be extremely grateful if you could take a look at our configuration, and perhaps identify what may have caused this problem.
I've now sent this same message as a support request; to your WPSEO Video, email address.